Unwarranted bill on account 6 months after closing it.

💢 T-MOBILE: I CANNOT CONTACT YOU AS MY PHONE NUMBER IS NO LONGER ASSOCIATED WITH MY ACCOUNT AND I CANNOT LOG IN TO PAY THE BILL YOU CLAIM I OWE. 💢

I closed my T-Mobile accounts in May of 2024 and have moved abroad. I cancelled my previous SIM and no longer have the phone number previously associated with T-Mobile. I just received a notice of an outstanding bill (with no description) after I had already closed my account in full and paid all remaining balances in June of 2024. It is now December of 2024, and I have no way of accessing my account to pay or close this problem as I cannot log in. 

I am unable to call as I do not have an international number at this time, and T-Mobile has made no attempt to contact me via email or my remaining contact methods. 

How do I contact T-Mobile to close my account permanently and have the bill waived? The bill is less than $12, and frankly not worth their time and the mail they will continue to send me for years. I paid in full and have receipts of such when I closed my accounts 6 months ago. 

Can anyone help?